The endoplasmic reticulum (ER) is a large network made of membranous cisternae and tubules, which accounts for a large proportion of the total lipid bilayer endomembrane of the cell. In mammals and yeast, LUNAPARK proteins are preferentially localized at the three-way junctions of the ER network, stabilizing the junctions and establishing the ER architecture. We identified two Arabidopsis homologs and designated them LNPA and LNPB. Subcellular localization analysis with a non-dimerizable type of green fluorescent protein (GFP) revealed that both LNPA and LNPB are predominantly distributed throughout the ER, but not preferentially localized at the three-way junctions. Quantitative analysis of the network in the double mutant lnpa lnpb revealed that deficiency of LNPA and LNPB caused the cortical ER to develop poor ER cisternae and a less dense tubular network. These phenotypes are opposite to those of LNP-deficient mutants of yeast and mammals. Despite the importance of cysteine residues in the zinc finger motif of the yeast LNP homolog (Lnp1p), the corresponding cysteine residues of LNPA were not necessary for the stabilization of ER morphology because replacing the four cysteine residues in the zinc finger motif of the LNPA protein with alanine residues did not affect its function. A significant phenotype of lnpa lnpb is generation of large spherical structures from the ER. Formation of the structures might reduce the amounts of the ER membrane to be used for generating the network, resulting in poor development of the ER network. Taken together, our results suggest that plant LNPs function differently from those in yeast and mammals: they function to distribute ER membranes appropriately throughout the cells.
Rakkasei-tofu (peanut-tofu) is a kind of a processed food which is made from peanut milk squeezed from ground peanut flour with water, starch and water. It is usually prepared using sweet potato starch in the Okinawa region. We made the Rakkasei-tofu from seven kinds of starches: kuzu starch, sweet potato starch, a low temperature gelatinization sweet potato starch called "minazuki", corn starch, tapioca starch and modified tapioca starches called "PB 108" and "PB 2000". The texture (hardness, cohesiveness and adhesiveness), degree of gelatinization and sensory evaluation were measured for each of these preparations. The physicochemical properties (particle size distribution, swelling power, solubility, X-ray diffraction, thermal properties using a differential scanning calorimetry; DSC and pasting properties using a Rapid Visco Analyzer; RVA) of the starches were also examined. It was demonstrated that Minazuki gelatinized at a low temperature similar to PB 108 and PB 2000. As the storage period increased, the cohesiveness and the gelatinization degree of the Rakkasei-tofu made from kuzu and sweet potato decreased, but those made from minazuki and PB 2000 retained higher cohesiveness and a greater degree of gelatinization. These results suggest that the Rakkasei-tofu made from starches showing low temperature gelatinization had good keeping qualities.
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